This application claims priority of European Patent Application No. 00302053.4, which was filed on Mar. 14, 2000.
The present invention relates to a reflective antenna structure, and particularly but not exclusively to a reflective antenna structure suitable for use in a so-called wireless fixed network.
In a fixed wireless network a location, such as a business premises or a residential premises, is provided with an antenna associated with a radio system for connection to a telephony network external to the premises. Within the premises, the antenna is connected to a fixed telephony system. In residential premises the fixed telephony system may be a single telephone. In a business premises the fixed telephony system may be a telephone network. Thus a fixed wireless network enables premises in remote locations. where connection to a fixed network infrastructure is difficult or expensive, to connect to such an infrastructure via a radio link.
Many fixed wireless systems rely on high gain directional antenna at a customer""s premises to improve system capacity. These antennas are either integrated into the customer""s premises unit, or are mounted separately with an RF cable.
In the former case, the gain of the antenna is fixed at manufacture. Such an integrated antenna is typically a planar or flat array antenna. Such an arrangement is inflexible due to the fixed gain which is built in at manufacture.
In the latter case, RF cable losses detract from the antenna gain. These losses become most significant at high frequencies ( greater than 2 GHz). Since the 3.4-3.6 GHz band is the favoured residential fixed wireless loop frequency allocation, cable losses can be significant, especially in low cost cables. An example of such an external antenna is a Yagi antenna, connected by RF cable. At 3.5 GHz cable losses make the implementation of such an antenna prohibitive.
It is an object of the present invention to provide an antenna arrangement, suitable for a fixed wireless system, in which the problems of the two known arrangements described hereinabove are overcome.
According to the present invention there is provided a reflective antenna having a DR (dielectric resonator) array as an integrated feed. The antenna may be a single reflector arrangement. The antenna may be a multi-reflector arrangement. The antenna may be a Cassegrain antenna.
A main reflector may clip onto the DR array. A sub-reflector may be supported by a radome mounted over the main reflector.
The reflective antenna may have a centre operating frequency of 3.5 GHz, in which the sub-reflector diameter is approximately 1.75 xcex and the main reflector diameter is approximately 5 xcex, an approximate 1.43 xcex separation distance being provided between the two reflectors.
A wireless communication system may incorporate such a reflective antenna.
A wireless local loop communication system, a wireless access communication system, or a wireless fixed network communication system may incorporate such a reflective antenna.
The invention described herein thus provides a field selectable antenna assembly, the gain of which can be matched to a particular application, without the need for an RF cable.
The invention involves a novel mechanical assembly incorporating, in a preferred embodiment, a technically advanced Cassegrain antenna design. The antenna achieves, in experiments, near theoretical performance with the minimum size.